path: root/deps/v8/src/runtime/runtime-array.cc

// Copyright 2014 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/v8.h"

#include "src/arguments.h"
#include "src/elements.h"
#include "src/messages.h"
#include "src/runtime/runtime-utils.h"

namespace v8 {
namespace internal {

RUNTIME_FUNCTION(Runtime_FinishArrayPrototypeSetup) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, prototype, 0);
  Object* length = prototype->length();
  RUNTIME_ASSERT(length->IsSmi() && Smi::cast(length)->value() == 0);
  RUNTIME_ASSERT(prototype->HasFastSmiOrObjectElements());
  // This is necessary to enable fast checks for absence of elements
  // on Array.prototype and below.
  prototype->set_elements(isolate->heap()->empty_fixed_array());
  return Smi::FromInt(0);
}


static void InstallBuiltin(Isolate* isolate, Handle<JSObject> holder,
                           const char* name, Builtins::Name builtin_name) {
  Handle<String> key = isolate->factory()->InternalizeUtf8String(name);
  Handle<Code> code(isolate->builtins()->builtin(builtin_name));
  Handle<JSFunction> optimized =
      isolate->factory()->NewFunctionWithoutPrototype(key, code);
  optimized->shared()->DontAdaptArguments();
  JSObject::AddProperty(holder, key, optimized, NONE);
}


RUNTIME_FUNCTION(Runtime_SpecialArrayFunctions) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 0);
  Handle<JSObject> holder =
      isolate->factory()->NewJSObject(isolate->object_function());

  InstallBuiltin(isolate, holder, "pop", Builtins::kArrayPop);
  InstallBuiltin(isolate, holder, "push", Builtins::kArrayPush);
  InstallBuiltin(isolate, holder, "shift", Builtins::kArrayShift);
  InstallBuiltin(isolate, holder, "unshift", Builtins::kArrayUnshift);
  InstallBuiltin(isolate, holder, "slice", Builtins::kArraySlice);
  InstallBuiltin(isolate, holder, "splice", Builtins::kArraySplice);
  InstallBuiltin(isolate, holder, "concat", Builtins::kArrayConcat);

  return *holder;
}


RUNTIME_FUNCTION(Runtime_FixedArrayGet) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 2);
  CONVERT_ARG_CHECKED(FixedArray, object, 0);
  CONVERT_SMI_ARG_CHECKED(index, 1);
  return object->get(index);
}


RUNTIME_FUNCTION(Runtime_FixedArraySet) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 3);
  CONVERT_ARG_CHECKED(FixedArray, object, 0);
  CONVERT_SMI_ARG_CHECKED(index, 1);
  CONVERT_ARG_CHECKED(Object, value, 2);
  object->set(index, value);
  return isolate->heap()->undefined_value();
}


RUNTIME_FUNCTION(Runtime_TransitionElementsKind) {
  HandleScope scope(isolate);
  RUNTIME_ASSERT(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, array, 0);
  CONVERT_ARG_HANDLE_CHECKED(Map, map, 1);
  JSObject::TransitionElementsKind(array, map->elements_kind());
  return *array;
}


// Push an object unto an array of objects if it is not already in the
// array.  Returns true if the element was pushed on the stack and
// false otherwise.
RUNTIME_FUNCTION(Runtime_PushIfAbsent) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, array, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSReceiver, element, 1);
  RUNTIME_ASSERT(array->HasFastSmiOrObjectElements());
  int length = Smi::cast(array->length())->value();
  FixedArray* elements = FixedArray::cast(array->elements());
  for (int i = 0; i < length; i++) {
    if (elements->get(i) == *element) return isolate->heap()->false_value();
  }

  // Strict not needed. Used for cycle detection in Array join implementation.
  RETURN_FAILURE_ON_EXCEPTION(
      isolate, JSObject::AddDataElement(array, length, element, NONE));
  JSObject::ValidateElements(array);
  return isolate->heap()->true_value();
}


/**
 * A simple visitor visits every element of Array's.
 * The backend storage can be a fixed array for fast elements case,
 * or a dictionary for sparse array. Since Dictionary is a subtype
 * of FixedArray, the class can be used by both fast and slow cases.
 * The second parameter of the constructor, fast_elements, specifies
 * whether the storage is a FixedArray or Dictionary.
 *
 * An index limit is used to deal with the situation that a result array
 * length overflows 32-bit non-negative integer.
 */
class ArrayConcatVisitor {
 public:
  ArrayConcatVisitor(Isolate* isolate, Handle<FixedArray> storage,
                     bool fast_elements)
      : isolate_(isolate),
        storage_(Handle<FixedArray>::cast(
            isolate->global_handles()->Create(*storage))),
        index_offset_(0u),
        bit_field_(FastElementsField::encode(fast_elements) |
                   ExceedsLimitField::encode(false)) {}

  ~ArrayConcatVisitor() { clear_storage(); }

  void visit(uint32_t i, Handle<Object> elm) {
    if (i > JSObject::kMaxElementCount - index_offset_) {
      set_exceeds_array_limit(true);
      return;
    }
    uint32_t index = index_offset_ + i;

    if (fast_elements()) {
      if (index < static_cast<uint32_t>(storage_->length())) {
        storage_->set(index, *elm);
        return;
      }
      // Our initial estimate of length was foiled, possibly by
      // getters on the arrays increasing the length of later arrays
      // during iteration.
      // This shouldn't happen in anything but pathological cases.
      SetDictionaryMode();
      // Fall-through to dictionary mode.
    }
    DCHECK(!fast_elements());
    Handle<SeededNumberDictionary> dict(
        SeededNumberDictionary::cast(*storage_));
    Handle<SeededNumberDictionary> result =
        SeededNumberDictionary::AtNumberPut(dict, index, elm);
    if (!result.is_identical_to(dict)) {
      // Dictionary needed to grow.
      clear_storage();
      set_storage(*result);
    }
  }

  void increase_index_offset(uint32_t delta) {
    if (JSObject::kMaxElementCount - index_offset_ < delta) {
      index_offset_ = JSObject::kMaxElementCount;
    } else {
      index_offset_ += delta;
    }
    // If the initial length estimate was off (see special case in visit()),
    // but the array blowing the limit didn't contain elements beyond the
    // provided-for index range, go to dictionary mode now.
    if (fast_elements() &&
        index_offset_ >
            static_cast<uint32_t>(FixedArrayBase::cast(*storage_)->length())) {
      SetDictionaryMode();
    }
  }

  bool exceeds_array_limit() const {
    return ExceedsLimitField::decode(bit_field_);
  }

  Handle<JSArray> ToArray() {
    Handle<JSArray> array = isolate_->factory()->NewJSArray(0);
    Handle<Object> length =
        isolate_->factory()->NewNumber(static_cast<double>(index_offset_));
    Handle<Map> map = JSObject::GetElementsTransitionMap(
        array, fast_elements() ? FAST_HOLEY_ELEMENTS : DICTIONARY_ELEMENTS);
    array->set_map(*map);
    array->set_length(*length);
    array->set_elements(*storage_);
    return array;
  }

 private:
  // Convert storage to dictionary mode.
  void SetDictionaryMode() {
    DCHECK(fast_elements());
    Handle<FixedArray> current_storage(*storage_);
    Handle<SeededNumberDictionary> slow_storage(
        SeededNumberDictionary::New(isolate_, current_storage->length()));
    uint32_t current_length = static_cast<uint32_t>(current_storage->length());
    for (uint32_t i = 0; i < current_length; i++) {
      HandleScope loop_scope(isolate_);
      Handle<Object> element(current_storage->get(i), isolate_);
      if (!element->IsTheHole()) {
        Handle<SeededNumberDictionary> new_storage =
            SeededNumberDictionary::AtNumberPut(slow_storage, i, element);
        if (!new_storage.is_identical_to(slow_storage)) {
          slow_storage = loop_scope.CloseAndEscape(new_storage);
        }
      }
    }
    clear_storage();
    set_storage(*slow_storage);
    set_fast_elements(false);
  }

  inline void clear_storage() {
    GlobalHandles::Destroy(Handle<Object>::cast(storage_).location());
  }

  inline void set_storage(FixedArray* storage) {
    storage_ =
        Handle<FixedArray>::cast(isolate_->global_handles()->Create(storage));
  }

  class FastElementsField : public BitField<bool, 0, 1> {};
  class ExceedsLimitField : public BitField<bool, 1, 1> {};

  bool fast_elements() const { return FastElementsField::decode(bit_field_); }
  void set_fast_elements(bool fast) {
    bit_field_ = FastElementsField::update(bit_field_, fast);
  }
  void set_exceeds_array_limit(bool exceeds) {
    bit_field_ = ExceedsLimitField::update(bit_field_, exceeds);
  }

  Isolate* isolate_;
  Handle<FixedArray> storage_;  // Always a global handle.
  // Index after last seen index. Always less than or equal to
  // JSObject::kMaxElementCount.
  uint32_t index_offset_;
  uint32_t bit_field_;
};


static uint32_t EstimateElementCount(Handle<JSArray> array) {
  uint32_t length = static_cast<uint32_t>(array->length()->Number());
  int element_count = 0;
  switch (array->GetElementsKind()) {
    case FAST_SMI_ELEMENTS:
    case FAST_HOLEY_SMI_ELEMENTS:
    case FAST_ELEMENTS:
    case FAST_HOLEY_ELEMENTS: {
      // Fast elements can't have lengths that are not representable by
      // a 32-bit signed integer.
      DCHECK(static_cast<int32_t>(FixedArray::kMaxLength) >= 0);
      int fast_length = static_cast<int>(length);
      Handle<FixedArray> elements(FixedArray::cast(array->elements()));
      for (int i = 0; i < fast_length; i++) {
        if (!elements->get(i)->IsTheHole()) element_count++;
      }
      break;
    }
    case FAST_DOUBLE_ELEMENTS:
    case FAST_HOLEY_DOUBLE_ELEMENTS: {
      // Fast elements can't have lengths that are not representable by
      // a 32-bit signed integer.
      DCHECK(static_cast<int32_t>(FixedDoubleArray::kMaxLength) >= 0);
      int fast_length = static_cast<int>(length);
      if (array->elements()->IsFixedArray()) {
        DCHECK(FixedArray::cast(array->elements())->length() == 0);
        break;
      }
      Handle<FixedDoubleArray> elements(
          FixedDoubleArray::cast(array->elements()));
      for (int i = 0; i < fast_length; i++) {
        if (!elements->is_the_hole(i)) element_count++;
      }
      break;
    }
    case DICTIONARY_ELEMENTS: {
      Handle<SeededNumberDictionary> dictionary(
          SeededNumberDictionary::cast(array->elements()));
      int capacity = dictionary->Capacity();
      for (int i = 0; i < capacity; i++) {
        Handle<Object> key(dictionary->KeyAt(i), array->GetIsolate());
        if (dictionary->IsKey(*key)) {
          element_count++;
        }
      }
      break;
    }
    case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
    case SLOW_SLOPPY_ARGUMENTS_ELEMENTS:
#define TYPED_ARRAY_CASE(Type, type, TYPE, ctype, size) \
  case EXTERNAL_##TYPE##_ELEMENTS:                      \
  case TYPE##_ELEMENTS:

      TYPED_ARRAYS(TYPED_ARRAY_CASE)
#undef TYPED_ARRAY_CASE
      // External arrays are always dense.
      return length;
  }
  // As an estimate, we assume that the prototype doesn't contain any
  // inherited elements.
  return element_count;
}


template <class ExternalArrayClass, class ElementType>
static void IterateTypedArrayElements(Isolate* isolate,
                                      Handle<JSObject> receiver,
                                      bool elements_are_ints,
                                      bool elements_are_guaranteed_smis,
                                      ArrayConcatVisitor* visitor) {
  Handle<ExternalArrayClass> array(
      ExternalArrayClass::cast(receiver->elements()));
  uint32_t len = static_cast<uint32_t>(array->length());

  DCHECK(visitor != NULL);
  if (elements_are_ints) {
    if (elements_are_guaranteed_smis) {
      for (uint32_t j = 0; j < len; j++) {
        HandleScope loop_scope(isolate);
        Handle<Smi> e(Smi::FromInt(static_cast<int>(array->get_scalar(j))),
                      isolate);
        visitor->visit(j, e);
      }
    } else {
      for (uint32_t j = 0; j < len; j++) {
        HandleScope loop_scope(isolate);
        int64_t val = static_cast<int64_t>(array->get_scalar(j));
        if (Smi::IsValid(static_cast<intptr_t>(val))) {
          Handle<Smi> e(Smi::FromInt(static_cast<int>(val)), isolate);
          visitor->visit(j, e);
        } else {
          Handle<Object> e =
              isolate->factory()->NewNumber(static_cast<ElementType>(val));
          visitor->visit(j, e);
        }
      }
    }
  } else {
    for (uint32_t j = 0; j < len; j++) {
      HandleScope loop_scope(isolate);
      Handle<Object> e = isolate->factory()->NewNumber(array->get_scalar(j));
      visitor->visit(j, e);
    }
  }
}


// Used for sorting indices in a List<uint32_t>.
static int compareUInt32(const uint32_t* ap, const uint32_t* bp) {
  uint32_t a = *ap;
  uint32_t b = *bp;
  return (a == b) ? 0 : (a < b) ? -1 : 1;
}


static void CollectElementIndices(Handle<JSObject> object, uint32_t range,
                                  List<uint32_t>* indices) {
  Isolate* isolate = object->GetIsolate();
  ElementsKind kind = object->GetElementsKind();
  switch (kind) {
    case FAST_SMI_ELEMENTS:
    case FAST_ELEMENTS:
    case FAST_HOLEY_SMI_ELEMENTS:
    case FAST_HOLEY_ELEMENTS: {
      Handle<FixedArray> elements(FixedArray::cast(object->elements()));
      uint32_t length = static_cast<uint32_t>(elements->length());
      if (range < length) length = range;
      for (uint32_t i = 0; i < length; i++) {
        if (!elements->get(i)->IsTheHole()) {
          indices->Add(i);
        }
      }
      break;
    }
    case FAST_HOLEY_DOUBLE_ELEMENTS:
    case FAST_DOUBLE_ELEMENTS: {
      if (object->elements()->IsFixedArray()) {
        DCHECK(object->elements()->length() == 0);
        break;
      }
      Handle<FixedDoubleArray> elements(
          FixedDoubleArray::cast(object->elements()));
      uint32_t length = static_cast<uint32_t>(elements->length());
      if (range < length) length = range;
      for (uint32_t i = 0; i < length; i++) {
        if (!elements->is_the_hole(i)) {
          indices->Add(i);
        }
      }
      break;
    }
    case DICTIONARY_ELEMENTS: {
      Handle<SeededNumberDictionary> dict(
          SeededNumberDictionary::cast(object->elements()));
      uint32_t capacity = dict->Capacity();
      for (uint32_t j = 0; j < capacity; j++) {
        HandleScope loop_scope(isolate);
        Handle<Object> k(dict->KeyAt(j), isolate);
        if (dict->IsKey(*k)) {
          DCHECK(k->IsNumber());
          uint32_t index = static_cast<uint32_t>(k->Number());
          if (index < range) {
            indices->Add(index);
          }
        }
      }
      break;
    }
#define TYPED_ARRAY_CASE(Type, type, TYPE, ctype, size) \
  case TYPE##_ELEMENTS:                                 \
  case EXTERNAL_##TYPE##_ELEMENTS:

      TYPED_ARRAYS(TYPED_ARRAY_CASE)
#undef TYPED_ARRAY_CASE
      {
        uint32_t length = static_cast<uint32_t>(
            FixedArrayBase::cast(object->elements())->length());
        if (range <= length) {
          length = range;
          // We will add all indices, so we might as well clear it first
          // and avoid duplicates.
          indices->Clear();
        }
        for (uint32_t i = 0; i < length; i++) {
          indices->Add(i);
        }
        if (length == range) return;  // All indices accounted for already.
        break;
      }
    case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
    case SLOW_SLOPPY_ARGUMENTS_ELEMENTS: {
      MaybeHandle<Object> length_obj =
          Object::GetProperty(object, isolate->factory()->length_string());
      double length_num = length_obj.ToHandleChecked()->Number();
      uint32_t length = static_cast<uint32_t>(DoubleToInt32(length_num));
      ElementsAccessor* accessor = object->GetElementsAccessor();
      for (uint32_t i = 0; i < length; i++) {
        if (accessor->HasElement(object, i)) {
          indices->Add(i);
        }
      }
      break;
    }
  }

  PrototypeIterator iter(isolate, object);
  if (!iter.IsAtEnd()) {
    // The prototype will usually have no inherited element indices,
    // but we have to check.
    CollectElementIndices(
        Handle<JSObject>::cast(PrototypeIterator::GetCurrent(iter)), range,
        indices);
  }
}


static bool IterateElementsSlow(Isolate* isolate, Handle<JSObject> receiver,
                                uint32_t length, ArrayConcatVisitor* visitor) {
  for (uint32_t i = 0; i < length; ++i) {
    HandleScope loop_scope(isolate);
    Maybe<bool> maybe = JSReceiver::HasElement(receiver, i);
    if (!maybe.IsJust()) return false;
    if (maybe.FromJust()) {
      Handle<Object> element_value;
      ASSIGN_RETURN_ON_EXCEPTION_VALUE(
          isolate, element_value,
          Runtime::GetElementOrCharAt(isolate, receiver, i), false);
      visitor->visit(i, element_value);
    }
  }
  visitor->increase_index_offset(length);
  return true;
}


/**
 * A helper function that visits elements of a JSObject in numerical
 * order.
 *
 * The visitor argument called for each existing element in the array
 * with the element index and the element's value.
 * Afterwards it increments the base-index of the visitor by the array
 * length.
 * Returns false if any access threw an exception, otherwise true.
 */
static bool IterateElements(Isolate* isolate, Handle<JSObject> receiver,
                            ArrayConcatVisitor* visitor) {
  uint32_t length = 0;

  if (receiver->IsJSArray()) {
    Handle<JSArray> array(Handle<JSArray>::cast(receiver));
    length = static_cast<uint32_t>(array->length()->Number());
  } else {
    Handle<Object> val;
    Handle<Object> key(isolate->heap()->length_string(), isolate);
    ASSIGN_RETURN_ON_EXCEPTION_VALUE(isolate, val,
        Runtime::GetObjectProperty(isolate, receiver, key), false);
    // TODO(caitp): Support larger element indexes (up to 2^53-1).
    if (!val->ToUint32(&length)) {
      ASSIGN_RETURN_ON_EXCEPTION_VALUE(isolate, val,
          Execution::ToLength(isolate, val), false);
      val->ToUint32(&length);
    }
  }

  if (!(receiver->IsJSArray() || receiver->IsJSTypedArray())) {
    // For classes which are not known to be safe to access via elements alone,
    // use the slow case.
    return IterateElementsSlow(isolate, receiver, length, visitor);
  }

  switch (receiver->GetElementsKind()) {
    case FAST_SMI_ELEMENTS:
    case FAST_ELEMENTS:
    case FAST_HOLEY_SMI_ELEMENTS:
    case FAST_HOLEY_ELEMENTS: {
      // Run through the elements FixedArray and use HasElement and GetElement
      // to check the prototype for missing elements.
      Handle<FixedArray> elements(FixedArray::cast(receiver->elements()));
      int fast_length = static_cast<int>(length);
      DCHECK(fast_length <= elements->length());
      for (int j = 0; j < fast_length; j++) {
        HandleScope loop_scope(isolate);
        Handle<Object> element_value(elements->get(j), isolate);
        if (!element_value->IsTheHole()) {
          visitor->visit(j, element_value);
        } else {
          Maybe<bool> maybe = JSReceiver::HasElement(receiver, j);
          if (!maybe.IsJust()) return false;
          if (maybe.FromJust()) {
            // Call GetElement on receiver, not its prototype, or getters won't
            // have the correct receiver.
            ASSIGN_RETURN_ON_EXCEPTION_VALUE(
                isolate, element_value,
                Object::GetElement(isolate, receiver, j), false);
            visitor->visit(j, element_value);
          }
        }
      }
      break;
    }
    case FAST_HOLEY_DOUBLE_ELEMENTS:
    case FAST_DOUBLE_ELEMENTS: {
      // Empty array is FixedArray but not FixedDoubleArray.
      if (length == 0) break;
      // Run through the elements FixedArray and use HasElement and GetElement
      // to check the prototype for missing elements.
      if (receiver->elements()->IsFixedArray()) {
        DCHECK(receiver->elements()->length() == 0);
        break;
      }
      Handle<FixedDoubleArray> elements(
          FixedDoubleArray::cast(receiver->elements()));
      int fast_length = static_cast<int>(length);
      DCHECK(fast_length <= elements->length());
      for (int j = 0; j < fast_length; j++) {
        HandleScope loop_scope(isolate);
        if (!elements->is_the_hole(j)) {
          double double_value = elements->get_scalar(j);
          Handle<Object> element_value =
              isolate->factory()->NewNumber(double_value);
          visitor->visit(j, element_value);
        } else {
          Maybe<bool> maybe = JSReceiver::HasElement(receiver, j);
          if (!maybe.IsJust()) return false;
          if (maybe.FromJust()) {
            // Call GetElement on receiver, not its prototype, or getters won't
            // have the correct receiver.
            Handle<Object> element_value;
            ASSIGN_RETURN_ON_EXCEPTION_VALUE(
                isolate, element_value,
                Object::GetElement(isolate, receiver, j), false);
            visitor->visit(j, element_value);
          }
        }
      }
      break;
    }
    case DICTIONARY_ELEMENTS: {
      Handle<SeededNumberDictionary> dict(receiver->element_dictionary());
      List<uint32_t> indices(dict->Capacity() / 2);
      // Collect all indices in the object and the prototypes less
      // than length. This might introduce duplicates in the indices list.
      CollectElementIndices(receiver, length, &indices);
      indices.Sort(&compareUInt32);
      int j = 0;
      int n = indices.length();
      while (j < n) {
        HandleScope loop_scope(isolate);
        uint32_t index = indices[j];
        Handle<Object> element;
        ASSIGN_RETURN_ON_EXCEPTION_VALUE(
            isolate, element, Object::GetElement(isolate, receiver, index),
            false);
        visitor->visit(index, element);
        // Skip to next different index (i.e., omit duplicates).
        do {
          j++;
        } while (j < n && indices[j] == index);
      }
      break;
    }
    case EXTERNAL_UINT8_CLAMPED_ELEMENTS: {
      Handle<ExternalUint8ClampedArray> pixels(
          ExternalUint8ClampedArray::cast(receiver->elements()));
      for (uint32_t j = 0; j < length; j++) {
        Handle<Smi> e(Smi::FromInt(pixels->get_scalar(j)), isolate);
        visitor->visit(j, e);
      }
      break;
    }
    case UINT8_CLAMPED_ELEMENTS: {
      Handle<FixedUint8ClampedArray> pixels(
      FixedUint8ClampedArray::cast(receiver->elements()));
      for (uint32_t j = 0; j < length; j++) {
        Handle<Smi> e(Smi::FromInt(pixels->get_scalar(j)), isolate);
        visitor->visit(j, e);
      }
      break;
    }
    case EXTERNAL_INT8_ELEMENTS: {
      IterateTypedArrayElements<ExternalInt8Array, int8_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case INT8_ELEMENTS: {
      IterateTypedArrayElements<FixedInt8Array, int8_t>(
      isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_UINT8_ELEMENTS: {
      IterateTypedArrayElements<ExternalUint8Array, uint8_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case UINT8_ELEMENTS: {
      IterateTypedArrayElements<FixedUint8Array, uint8_t>(
      isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_INT16_ELEMENTS: {
      IterateTypedArrayElements<ExternalInt16Array, int16_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case INT16_ELEMENTS: {
      IterateTypedArrayElements<FixedInt16Array, int16_t>(
      isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_UINT16_ELEMENTS: {
      IterateTypedArrayElements<ExternalUint16Array, uint16_t>(
          isolate, receiver, true, true, visitor);
      break;
    }
    case UINT16_ELEMENTS: {
      IterateTypedArrayElements<FixedUint16Array, uint16_t>(
      isolate, receiver, true, true, visitor);
      break;
    }
    case EXTERNAL_INT32_ELEMENTS: {
      IterateTypedArrayElements<ExternalInt32Array, int32_t>(
          isolate, receiver, true, false, visitor);
      break;
    }
    case INT32_ELEMENTS: {
      IterateTypedArrayElements<FixedInt32Array, int32_t>(
      isolate, receiver, true, false, visitor);
      break;
    }
    case EXTERNAL_UINT32_ELEMENTS: {
      IterateTypedArrayElements<ExternalUint32Array, uint32_t>(
          isolate, receiver, true, false, visitor);
      break;
    }
    case UINT32_ELEMENTS: {
      IterateTypedArrayElements<FixedUint32Array, uint32_t>(
      isolate, receiver, true, false, visitor);
      break;
    }
    case EXTERNAL_FLOAT32_ELEMENTS: {
      IterateTypedArrayElements<ExternalFloat32Array, float>(
          isolate, receiver, false, false, visitor);
      break;
    }
    case FLOAT32_ELEMENTS: {
      IterateTypedArrayElements<FixedFloat32Array, float>(
      isolate, receiver, false, false, visitor);
      break;
    }
    case EXTERNAL_FLOAT64_ELEMENTS: {
      IterateTypedArrayElements<ExternalFloat64Array, double>(
          isolate, receiver, false, false, visitor);
      break;
    }
    case FLOAT64_ELEMENTS: {
      IterateTypedArrayElements<FixedFloat64Array, double>(
      isolate, receiver, false, false, visitor);
      break;
    }
    case FAST_SLOPPY_ARGUMENTS_ELEMENTS:
    case SLOW_SLOPPY_ARGUMENTS_ELEMENTS: {
      for (uint32_t index = 0; index < length; index++) {
        HandleScope loop_scope(isolate);
        Handle<Object> element;
        ASSIGN_RETURN_ON_EXCEPTION_VALUE(
            isolate, element, Object::GetElement(isolate, receiver, index),
            false);
        visitor->visit(index, element);
      }
      break;
    }
  }
  visitor->increase_index_offset(length);
  return true;
}


static bool IsConcatSpreadable(Isolate* isolate, Handle<Object> obj) {
  HandleScope handle_scope(isolate);
  if (!obj->IsSpecObject()) return false;
  if (FLAG_harmony_concat_spreadable) {
    Handle<Symbol> key(isolate->factory()->is_concat_spreadable_symbol());
    Handle<Object> value;
    MaybeHandle<Object> maybeValue =
        i::Runtime::GetObjectProperty(isolate, obj, key);
    if (maybeValue.ToHandle(&value)) {
      if (!value->IsUndefined()) {
        return value->BooleanValue();
      }
    }
  }
  return obj->IsJSArray();
}


/**
 * Array::concat implementation.
 * See ECMAScript 262, 15.4.4.4.
 * TODO(581): Fix non-compliance for very large concatenations and update to
 * following the ECMAScript 5 specification.
 */
RUNTIME_FUNCTION(Runtime_ArrayConcat) {
  HandleScope handle_scope(isolate);
  DCHECK(args.length() == 1);

  CONVERT_ARG_HANDLE_CHECKED(JSArray, arguments, 0);
  int argument_count = static_cast<int>(arguments->length()->Number());
  RUNTIME_ASSERT(arguments->HasFastObjectElements());
  Handle<FixedArray> elements(FixedArray::cast(arguments->elements()));

  // Pass 1: estimate the length and number of elements of the result.
  // The actual length can be larger if any of the arguments have getters
  // that mutate other arguments (but will otherwise be precise).
  // The number of elements is precise if there are no inherited elements.

  ElementsKind kind = FAST_SMI_ELEMENTS;

  uint32_t estimate_result_length = 0;
  uint32_t estimate_nof_elements = 0;
  for (int i = 0; i < argument_count; i++) {
    HandleScope loop_scope(isolate);
    Handle<Object> obj(elements->get(i), isolate);
    uint32_t length_estimate;
    uint32_t element_estimate;
    if (obj->IsJSArray()) {
      Handle<JSArray> array(Handle<JSArray>::cast(obj));
      length_estimate = static_cast<uint32_t>(array->length()->Number());
      if (length_estimate != 0) {
        ElementsKind array_kind =
            GetPackedElementsKind(array->map()->elements_kind());
        if (IsMoreGeneralElementsKindTransition(kind, array_kind)) {
          kind = array_kind;
        }
      }
      element_estimate = EstimateElementCount(array);
    } else {
      if (obj->IsHeapObject()) {
        if (obj->IsNumber()) {
          if (IsMoreGeneralElementsKindTransition(kind, FAST_DOUBLE_ELEMENTS)) {
            kind = FAST_DOUBLE_ELEMENTS;
          }
        } else if (IsMoreGeneralElementsKindTransition(kind, FAST_ELEMENTS)) {
          kind = FAST_ELEMENTS;
        }
      }
      length_estimate = 1;
      element_estimate = 1;
    }
    // Avoid overflows by capping at kMaxElementCount.
    if (JSObject::kMaxElementCount - estimate_result_length < length_estimate) {
      estimate_result_length = JSObject::kMaxElementCount;
    } else {
      estimate_result_length += length_estimate;
    }
    if (JSObject::kMaxElementCount - estimate_nof_elements < element_estimate) {
      estimate_nof_elements = JSObject::kMaxElementCount;
    } else {
      estimate_nof_elements += element_estimate;
    }
  }

  // If estimated number of elements is more than half of length, a
  // fixed array (fast case) is more time and space-efficient than a
  // dictionary.
  bool fast_case = (estimate_nof_elements * 2) >= estimate_result_length;

  if (fast_case && kind == FAST_DOUBLE_ELEMENTS) {
    Handle<FixedArrayBase> storage =
        isolate->factory()->NewFixedDoubleArray(estimate_result_length);
    int j = 0;
    bool failure = false;
    if (estimate_result_length > 0) {
      Handle<FixedDoubleArray> double_storage =
          Handle<FixedDoubleArray>::cast(storage);
      for (int i = 0; i < argument_count; i++) {
        Handle<Object> obj(elements->get(i), isolate);
        if (obj->IsSmi()) {
          double_storage->set(j, Smi::cast(*obj)->value());
          j++;
        } else if (obj->IsNumber()) {
          double_storage->set(j, obj->Number());
          j++;
        } else {
          JSArray* array = JSArray::cast(*obj);
          uint32_t length = static_cast<uint32_t>(array->length()->Number());
          switch (array->map()->elements_kind()) {
            case FAST_HOLEY_DOUBLE_ELEMENTS:
            case FAST_DOUBLE_ELEMENTS: {
              // Empty array is FixedArray but not FixedDoubleArray.
              if (length == 0) break;
              FixedDoubleArray* elements =
                  FixedDoubleArray::cast(array->elements());
              for (uint32_t i = 0; i < length; i++) {
                if (elements->is_the_hole(i)) {
                  // TODO(jkummerow/verwaest): We could be a bit more clever
                  // here: Check if there are no elements/getters on the
                  // prototype chain, and if so, allow creation of a holey
                  // result array.
                  // Same thing below (holey smi case).
                  failure = true;
                  break;
                }
                double double_value = elements->get_scalar(i);
                double_storage->set(j, double_value);
                j++;
              }
              break;
            }
            case FAST_HOLEY_SMI_ELEMENTS:
            case FAST_SMI_ELEMENTS: {
              FixedArray* elements(FixedArray::cast(array->elements()));
              for (uint32_t i = 0; i < length; i++) {
                Object* element = elements->get(i);
                if (element->IsTheHole()) {
                  failure = true;
                  break;
                }
                int32_t int_value = Smi::cast(element)->value();
                double_storage->set(j, int_value);
                j++;
              }
              break;
            }
            case FAST_HOLEY_ELEMENTS:
            case FAST_ELEMENTS:
            case DICTIONARY_ELEMENTS:
              DCHECK_EQ(0u, length);
              break;
            default:
              UNREACHABLE();
          }
        }
        if (failure) break;
      }
    }
    if (!failure) {
      Handle<JSArray> array = isolate->factory()->NewJSArray(0);
      Smi* length = Smi::FromInt(j);
      Handle<Map> map;
      map = JSObject::GetElementsTransitionMap(array, kind);
      array->set_map(*map);
      array->set_length(length);
      array->set_elements(*storage);
      return *array;
    }
    // In case of failure, fall through.
  }

  Handle<FixedArray> storage;
  if (fast_case) {
    // The backing storage array must have non-existing elements to preserve
    // holes across concat operations.
    storage =
        isolate->factory()->NewFixedArrayWithHoles(estimate_result_length);
  } else {
    // TODO(126): move 25% pre-allocation logic into Dictionary::Allocate
    uint32_t at_least_space_for =
        estimate_nof_elements + (estimate_nof_elements >> 2);
    storage = Handle<FixedArray>::cast(
        SeededNumberDictionary::New(isolate, at_least_space_for));
  }

  ArrayConcatVisitor visitor(isolate, storage, fast_case);

  for (int i = 0; i < argument_count; i++) {
    Handle<Object> obj(elements->get(i), isolate);
    bool spreadable = IsConcatSpreadable(isolate, obj);
    if (isolate->has_pending_exception()) return isolate->heap()->exception();
    if (spreadable) {
      Handle<JSObject> object = Handle<JSObject>::cast(obj);
      if (!IterateElements(isolate, object, &visitor)) {
        return isolate->heap()->exception();
      }
    } else {
      visitor.visit(0, obj);
      visitor.increase_index_offset(1);
    }
  }

  if (visitor.exceeds_array_limit()) {
    THROW_NEW_ERROR_RETURN_FAILURE(
        isolate, NewRangeError(MessageTemplate::kInvalidArrayLength));
  }
  return *visitor.ToArray();
}


// Moves all own elements of an object, that are below a limit, to positions
// starting at zero. All undefined values are placed after non-undefined values,
// and are followed by non-existing element. Does not change the length
// property.
// Returns the number of non-undefined elements collected.
// Returns -1 if hole removal is not supported by this method.
RUNTIME_FUNCTION(Runtime_RemoveArrayHoles) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
  CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[1]);
  return *JSObject::PrepareElementsForSort(object, limit);
}


// Move contents of argument 0 (an array) to argument 1 (an array)
RUNTIME_FUNCTION(Runtime_MoveArrayContents) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, from, 0);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, to, 1);
  JSObject::ValidateElements(from);
  JSObject::ValidateElements(to);

  Handle<FixedArrayBase> new_elements(from->elements());
  ElementsKind from_kind = from->GetElementsKind();
  Handle<Map> new_map = JSObject::GetElementsTransitionMap(to, from_kind);
  JSObject::SetMapAndElements(to, new_map, new_elements);
  to->set_length(from->length());

  JSObject::ResetElements(from);
  from->set_length(Smi::FromInt(0));

  JSObject::ValidateElements(to);
  return *to;
}


// How many elements does this object/array have?
RUNTIME_FUNCTION(Runtime_EstimateNumberOfElements) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSArray, array, 0);
  Handle<FixedArrayBase> elements(array->elements(), isolate);
  SealHandleScope shs(isolate);
  if (elements->IsDictionary()) {
    int result =
        Handle<SeededNumberDictionary>::cast(elements)->NumberOfElements();
    return Smi::FromInt(result);
  } else {
    DCHECK(array->length()->IsSmi());
    // For packed elements, we know the exact number of elements
    int length = elements->length();
    ElementsKind kind = array->GetElementsKind();
    if (IsFastPackedElementsKind(kind)) {
      return Smi::FromInt(length);
    }
    // For holey elements, take samples from the buffer checking for holes
    // to generate the estimate.
    const int kNumberOfHoleCheckSamples = 97;
    int increment = (length < kNumberOfHoleCheckSamples)
                        ? 1
                        : static_cast<int>(length / kNumberOfHoleCheckSamples);
    ElementsAccessor* accessor = array->GetElementsAccessor();
    int holes = 0;
    for (int i = 0; i < length; i += increment) {
      if (!accessor->HasElement(array, i, elements)) {
        ++holes;
      }
    }
    int estimate = static_cast<int>((kNumberOfHoleCheckSamples - holes) /
                                    kNumberOfHoleCheckSamples * length);
    return Smi::FromInt(estimate);
  }
}


// Returns an array that tells you where in the [0, length) interval an array
// might have elements.  Can either return an array of keys (positive integers
// or undefined) or a number representing the positive length of an interval
// starting at index 0.
// Intervals can span over some keys that are not in the object.
RUNTIME_FUNCTION(Runtime_GetArrayKeys) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, array, 0);
  CONVERT_NUMBER_CHECKED(uint32_t, length, Uint32, args[1]);
  if (array->elements()->IsDictionary()) {
    Handle<FixedArray> keys = isolate->factory()->empty_fixed_array();
    for (PrototypeIterator iter(isolate, array,
                                PrototypeIterator::START_AT_RECEIVER);
         !iter.IsAtEnd(); iter.Advance()) {
      if (PrototypeIterator::GetCurrent(iter)->IsJSProxy() ||
          JSObject::cast(*PrototypeIterator::GetCurrent(iter))
              ->HasIndexedInterceptor()) {
        // Bail out if we find a proxy or interceptor, likely not worth
        // collecting keys in that case.
        return *isolate->factory()->NewNumberFromUint(length);
      }
      Handle<JSObject> current =
          Handle<JSObject>::cast(PrototypeIterator::GetCurrent(iter));
      Handle<FixedArray> current_keys =
          isolate->factory()->NewFixedArray(current->NumberOfOwnElements(NONE));
      current->GetOwnElementKeys(*current_keys, NONE);
      ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
          isolate, keys, FixedArray::UnionOfKeys(keys, current_keys));
    }
    // Erase any keys >= length.
    // TODO(adamk): Remove this step when the contract of %GetArrayKeys
    // is changed to let this happen on the JS side.
    for (int i = 0; i < keys->length(); i++) {
      if (NumberToUint32(keys->get(i)) >= length) keys->set_undefined(i);
    }
    return *isolate->factory()->NewJSArrayWithElements(keys);
  } else {
    RUNTIME_ASSERT(array->HasFastSmiOrObjectElements() ||
                   array->HasFastDoubleElements());
    uint32_t actual_length = static_cast<uint32_t>(array->elements()->length());
    return *isolate->factory()->NewNumberFromUint(Min(actual_length, length));
  }
}


static Object* ArrayConstructorCommon(Isolate* isolate,
                                      Handle<JSFunction> constructor,
                                      Handle<JSFunction> original_constructor,
                                      Handle<AllocationSite> site,
                                      Arguments* caller_args) {
  Factory* factory = isolate->factory();

  bool holey = false;
  bool can_use_type_feedback = true;
  bool can_inline_array_constructor = true;
  if (caller_args->length() == 1) {
    Handle<Object> argument_one = caller_args->at<Object>(0);
    if (argument_one->IsSmi()) {
      int value = Handle<Smi>::cast(argument_one)->value();
      if (value < 0 ||
          JSArray::SetLengthWouldNormalize(isolate->heap(), value)) {
        // the array is a dictionary in this case.
        can_use_type_feedback = false;
      } else if (value != 0) {
        holey = true;
        if (value >= JSObject::kInitialMaxFastElementArray) {
          can_inline_array_constructor = false;
        }
      }
    } else {
      // Non-smi length argument produces a dictionary
      can_use_type_feedback = false;
    }
  }

  Handle<JSArray> array;
  if (!site.is_null() && can_use_type_feedback) {
    ElementsKind to_kind = site->GetElementsKind();
    if (holey && !IsFastHoleyElementsKind(to_kind)) {
      to_kind = GetHoleyElementsKind(to_kind);
      // Update the allocation site info to reflect the advice alteration.
      site->SetElementsKind(to_kind);
    }

    // We should allocate with an initial map that reflects the allocation site
    // advice. Therefore we use AllocateJSObjectFromMap instead of passing
    // the constructor.
    Handle<Map> initial_map(constructor->initial_map(), isolate);
    if (to_kind != initial_map->elements_kind()) {
      initial_map = Map::AsElementsKind(initial_map, to_kind);
    }

    // If we don't care to track arrays of to_kind ElementsKind, then
    // don't emit a memento for them.
    Handle<AllocationSite> allocation_site;
    if (AllocationSite::GetMode(to_kind) == TRACK_ALLOCATION_SITE) {
      allocation_site = site;
    }

    array = Handle<JSArray>::cast(factory->NewJSObjectFromMap(
        initial_map, NOT_TENURED, true, allocation_site));
  } else {
    array = Handle<JSArray>::cast(factory->NewJSObject(constructor));

    // We might need to transition to holey
    ElementsKind kind = constructor->initial_map()->elements_kind();
    if (holey && !IsFastHoleyElementsKind(kind)) {
      kind = GetHoleyElementsKind(kind);
      JSObject::TransitionElementsKind(array, kind);
    }
  }

  factory->NewJSArrayStorage(array, 0, 0, DONT_INITIALIZE_ARRAY_ELEMENTS);

  ElementsKind old_kind = array->GetElementsKind();
  RETURN_FAILURE_ON_EXCEPTION(
      isolate, ArrayConstructInitializeElements(array, caller_args));
  if (!site.is_null() &&
      (old_kind != array->GetElementsKind() || !can_use_type_feedback ||
       !can_inline_array_constructor)) {
    // The arguments passed in caused a transition. This kind of complexity
    // can't be dealt with in the inlined hydrogen array constructor case.
    // We must mark the allocationsite as un-inlinable.
    site->SetDoNotInlineCall();
  }

  // Set up the prototoype using original function.
  // TODO(dslomov): instead of setting the __proto__,
  // use and cache the correct map.
  if (*original_constructor != *constructor) {
    if (original_constructor->has_instance_prototype()) {
      Handle<Object> prototype =
          handle(original_constructor->instance_prototype(), isolate);
      RETURN_FAILURE_ON_EXCEPTION(
          isolate, JSObject::SetPrototype(array, prototype, false));
    }
  }

  return *array;
}


RUNTIME_FUNCTION(Runtime_ArrayConstructor) {
  HandleScope scope(isolate);
  // If we get 2 arguments then they are the stub parameters (constructor, type
  // info).  If we get 4, then the first one is a pointer to the arguments
  // passed by the caller, and the last one is the length of the arguments
  // passed to the caller (redundant, but useful to check on the deoptimizer
  // with an assert).
  Arguments empty_args(0, NULL);
  bool no_caller_args = args.length() == 2;
  DCHECK(no_caller_args || args.length() == 4);
  int parameters_start = no_caller_args ? 0 : 1;
  Arguments* caller_args =
      no_caller_args ? &empty_args : reinterpret_cast<Arguments*>(args[0]);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, constructor, parameters_start);
  CONVERT_ARG_HANDLE_CHECKED(Object, type_info, parameters_start + 1);
#ifdef DEBUG
  if (!no_caller_args) {
    CONVERT_SMI_ARG_CHECKED(arg_count, parameters_start + 2);
    DCHECK(arg_count == caller_args->length());
  }
#endif

  Handle<AllocationSite> site;
  if (!type_info.is_null() &&
      *type_info != isolate->heap()->undefined_value()) {
    site = Handle<AllocationSite>::cast(type_info);
    DCHECK(!site->SitePointsToLiteral());
  }

  return ArrayConstructorCommon(isolate, constructor, constructor, site,
                                caller_args);
}


RUNTIME_FUNCTION(Runtime_ArrayConstructorWithSubclassing) {
  HandleScope scope(isolate);
  int args_length = args.length();
  CHECK(args_length >= 2);

  // This variables and checks work around -Werror=strict-overflow.
  int pre_last_arg_index = args_length - 2;
  int last_arg_index = args_length - 1;
  CHECK(pre_last_arg_index >= 0);
  CHECK(last_arg_index >= 0);

  CONVERT_ARG_HANDLE_CHECKED(JSFunction, constructor, pre_last_arg_index);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, original_constructor, last_arg_index);
  Arguments caller_args(args_length - 2, args.arguments());
  return ArrayConstructorCommon(isolate, constructor, original_constructor,
                                Handle<AllocationSite>::null(), &caller_args);
}


RUNTIME_FUNCTION(Runtime_InternalArrayConstructor) {
  HandleScope scope(isolate);
  Arguments empty_args(0, NULL);
  bool no_caller_args = args.length() == 1;
  DCHECK(no_caller_args || args.length() == 3);
  int parameters_start = no_caller_args ? 0 : 1;
  Arguments* caller_args =
      no_caller_args ? &empty_args : reinterpret_cast<Arguments*>(args[0]);
  CONVERT_ARG_HANDLE_CHECKED(JSFunction, constructor, parameters_start);
#ifdef DEBUG
  if (!no_caller_args) {
    CONVERT_SMI_ARG_CHECKED(arg_count, parameters_start + 1);
    DCHECK(arg_count == caller_args->length());
  }
#endif
  return ArrayConstructorCommon(isolate, constructor, constructor,
                                Handle<AllocationSite>::null(), caller_args);
}


RUNTIME_FUNCTION(Runtime_NormalizeElements) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, array, 0);
  RUNTIME_ASSERT(!array->HasExternalArrayElements() &&
                 !array->HasFixedTypedArrayElements() &&
                 !array->IsJSGlobalProxy());
  JSObject::NormalizeElements(array);
  return *array;
}


// GrowArrayElements returns a sentinel Smi if the object was normalized.
RUNTIME_FUNCTION(Runtime_GrowArrayElements) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 2);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
  CONVERT_NUMBER_CHECKED(int, key, Int32, args[1]);

  if (key < 0) {
    return object->elements();
  }

  uint32_t capacity = static_cast<uint32_t>(object->elements()->length());
  uint32_t index = static_cast<uint32_t>(key);

  if (index >= capacity) {
    if (object->WouldConvertToSlowElements(index)) {
      // We don't want to allow operations that cause lazy deopt. Return a Smi
      // as a signal that optimized code should eagerly deoptimize.
      return Smi::FromInt(0);
    }

    uint32_t new_capacity = JSObject::NewElementsCapacity(index + 1);
    object->GetElementsAccessor()->GrowCapacityAndConvert(object, new_capacity);
  }

  // On success, return the fixed array elements.
  return object->elements();
}


RUNTIME_FUNCTION(Runtime_HasComplexElements) {
  HandleScope scope(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_HANDLE_CHECKED(JSObject, array, 0);
  for (PrototypeIterator iter(isolate, array,
                              PrototypeIterator::START_AT_RECEIVER);
       !iter.IsAtEnd(); iter.Advance()) {
    if (PrototypeIterator::GetCurrent(iter)->IsJSProxy()) {
      return isolate->heap()->true_value();
    }
    Handle<JSObject> current =
        Handle<JSObject>::cast(PrototypeIterator::GetCurrent(iter));
    if (current->HasIndexedInterceptor()) {
      return isolate->heap()->true_value();
    }
    if (!current->HasDictionaryElements()) continue;
    if (current->element_dictionary()->HasComplexElements()) {
      return isolate->heap()->true_value();
    }
  }
  return isolate->heap()->false_value();
}


RUNTIME_FUNCTION(Runtime_IsArray) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 1);
  CONVERT_ARG_CHECKED(Object, obj, 0);
  return isolate->heap()->ToBoolean(obj->IsJSArray());
}


RUNTIME_FUNCTION(Runtime_HasCachedArrayIndex) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 1);
  return isolate->heap()->false_value();
}


RUNTIME_FUNCTION(Runtime_GetCachedArrayIndex) {
  // This can never be reached, because Runtime_HasCachedArrayIndex always
  // returns false.
  UNIMPLEMENTED();
  return nullptr;
}


RUNTIME_FUNCTION(Runtime_FastOneByteArrayJoin) {
  SealHandleScope shs(isolate);
  DCHECK(args.length() == 2);
  // Returning undefined means that this fast path fails and one has to resort
  // to a slow path.
  return isolate->heap()->undefined_value();
}
}  // namespace internal
}  // namespace v8